In known electro-hydraulic control systems, electronic control devices are allocated to the individual roof supports together with valves assembled as valve blocks. The valves consist of or include direction control valves which are connected on the inlet side to an hydraulic pressure and return line and on the outlet side to the working chambers of hydraulic appliances.
Electro-hydraulic support control systems of various designs are known (See "Gluckauf" 1981, pages 155-162; "Gluckauf" 1984, pages 135-140; "Gluckauf" 1986, pages 1183-1187). In modern mining practice, preference is given to control systems which are decentralised and in which each roof support along the longwall face is provided with an individual electronic control device with a microprocessor. The individual control devices are then coupled to one another and optionally also to a central control station via data transmission cables. The individual control devices are each provided with an operator's access station with a keyboard, by means of which various control processes can be initiated. The system is supplied with power by means of intrinsically safe power sources, and an electronic control device or a group of electronic control devices can be connected to each power source.
To achieve the intrinsic safety required in underground mining with minimum consumption of electric energy, it is known from DE-OS 35 30 657 to use electrically controllable solenoid valves as pilot valves in the hydraulic control lines of the direction control valves in such a way that these direction control valves are controlled solely by the pilot valves which can be switched without pressure by electrical energy. The valves of the support which are combined to form valve blocks therefore comprise, in addition to the hydraulically controllable direction control valves, a number of solenoid valves which can be electrically controlled individually or in groups by the associated control device. This control system performs satisfactorily during normal conditions but electrical faults or power failure can disable the system and can result in danger to personnel. An object of the invention is to provide a simple emergency arrangement for an electro-hydraulic control system, with which at least the most important functions of the supports can be intentionally and reliably controlled from a safe position even during a power failure or during a failure of the electronic controls.